Body Fat Measures

Measuring your body fat is an important way of evaluating your diet and your training. No technique is accurate and all approaches are estimates based on indirect measures. However, there are a number of cost effective and practical approaches you can use.

1 Skinfold Calipers

Main article: Skinfold Calipers

This is the cheapest way of getting a viable estimate of your own body fat. The calipers are extremely cheap ($5 from Amazon.com) and directly measure your body fat. They do require some practice to get repeatable results, but the price, performance and convenience makes them an ideal starting point.

Accu-measure calipers in action

2 Body Fat Scales

These Bioelectrical Impedance Analysis (BIA) scales use an imperceptible electrical signal to calculate the amount of water in the body. From this Total Body Water (TBW), it is possible to estimate body fat. This makes these scales quick and easy to use, but their accuracy is quite poor. The level of hydration has a significant impact on the reading, so readings need to be taken at the same time of day with the same level of hydration. The 4 Hour Body recommend drinking 1.5 liters (3 pints) of water, waiting 30 minutes, urinating and then taking a measurement. The biggest problem for an athlete is that BIA is particularly inaccurate when fat free mass, including glycogen, changes. I've noticed that the day after a long run, the scales claim a much larger loss of body fat than is reasonable.

I categorize these scales into three types.

2.1 Lower Body Only

Most body fat scales have electrodes only on the feet, so the electric current only goes from one foot to the other. This only measures the lower part of the body, not the whole body. I have the Tanita BF680 which retails for $60.

2.2 Full Body BIA Scales

These scales also use BIA, but have electrodes on the hands as well as the feet, giving a measure across the whole body. In my experience, these scales show changes in body fat far better than the BIA scales that read from the feet only. I have the Omron HBF-510 which retail for $60.

2.3 Segmental Body Fat Scales

The latest Tanita scales use two frequencies of electrical signal and use electrodes for the hands and feet. I have not tried these scales as they are expensive ($300). If these scales could transfer the measurements to a PC via bluetooth, I'd be tempted to get one.

2.4 Comparison of Lower Body and Full Body Scales

Over the years I have found lower body scales show that weight loss is disproportionately from non-fat when other measures show fat levels stayed constant or dropped. Here is a recent comparison of weight loss indications from the Tanita and Omron. As you can see, the Omron shows a higher level of fat loss than the Tanita, and I believe that the Omron is more accurate. Notice the large day to day variations; this is why I measure every day and look at the overall average. I use a moving seven day average (the dotted lines) to evaluate the overall progress.

3 BOD POD

This is a chamber that works out your body volume accurately. Given the volume and weight you have the density, from which you can estimate body composition. The test costs about $25 at a gym, which makes it expensive to use regularly. I believe there are two types of BOD POD, a recreational and a research model. The recreational model is used by many gyms and estimates lung function, whereas the research model actually measures lung volume. I found the BOD POD quick and easy, but requires a trip to a gym. The cost means that I do not have a sense of how the reading changes over time, and its correlation with other techniques. See http://www.bodpod.com/ for more details.

4 Underwater Weighing

This used to be the 'gold standard' of body fat measurement. The technique involves being weighed on dry ground and then again underwater having breathed out as much as possible. This gives a value of density, so it should have similar accuracy as the BOD POD, but is more expensive and unpleasant. I have not tried this technique.

5 DEXA

Different tissues in the body absorb different frequencies of X-Rays at different levels. This technique (Deal-Energy X-Ray Absorpiometry) uses two frequencies of X-Rays and looks at the different absorption to work out body fat. This is the current 'gold standard' and I believe it will show the distribution of body fat as well as the level. I have not found anywhere locally that provides DEXA.

6 Alternatives to Measurement

These approaches can give some hint about your body fat, but are no substitute for a real measurement.

6.1 Waist to Hips Ratio

This does not directly measure body fat, but is a crude measure of health. A ratio of 0.7 for women and 0.9 for men is correlated with good health. This is a crude measure, but can be useful for an initial evaluation.

6.2 Body Mass Index

This is a simple figure based on your height and weight, and gives no real indication of body fat. If you are overweight it can give a sense of your health risk, but overall it's quite useless.

6.3 Mirror

Looking at yourself in a mirror is a simple method that can give a sense of body fat. Obviously there is no numerical quantity to this test, but it's cheap and easy.

6.4 Abdominal Muscle Definition

If your body fat is low enough, the definition in your abdominal muscles (six pack) can be used to monitor body fat changes. There is no specific body fat percentage for having a six-pack, but the common thought is that you need to be 12-8% for men and 18-14 for women.